Abstract
An instrument capable of collocated measurement of three perpendicular ground velocity components (two horizontal and one vertical), three seismic rotation rate components (around two horizontal axes and one vertical) and three strain components in a high-frequency range of 2-100 Hz. Compared to the older prototypes, three new ground-motion components (strains) are measured by laser dilatometers.
Further, the maximum measurable frequency of seismic motions has been increased by suppressing undesirable resonances due to a changed shape of the rigid metal frame of the instrument. Moreover, the accuracy of the rotational measurement has been significantly increased by using more sensitive geophones in an innovated arrangement and by applying a newly developed method of calibration of the geophones in the system.